Production of tetrabasic lead sulfate from solid state reactions for the preparation of active plates to be used in lead-acid batteries

ABSTRACT

A solid state reaction method for the production of tetrabasic lead sulfate includes the steps of mixing a stoichiometric mixture of 4PbO and PbCO 3  and H 2 SO 4  and heating the stoichiometric mixture of 4PbO and PbCO 3  and H 2 SO 4  at a temperature between 500 and 700° C. for 3 to 8 hours. The method also includes the steps of deagglomerating and sieving resulting tetrabasic lead sulfate.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a Divisional of U.S. application Ser. No.11/296,130, filed Dec. 7, 2005, which is a Divisional of U.S.application Ser. No. 10/803,491, filed Mar. 19, 2004, both of which areincorporated herein by reference in their entirety.

BACKGROUND

This invention relates generally to the production of tetrabasic leadsulfate and more specifically to the production of tetrabasic leadsulfate from solid state reactions for the preparation of active platesto be used in lead-acid batteries.

The preparation of active electrodes or plates for lead-acid batteriesinvolves three steps: a) paste application to a supporting grid, b)drying and curing of the pasted grid, and c) electrochemical formationof the cured grid to produce the active materials used in the chargedlead-acid battery. Battery formation is usually carried out by passingcurrent through the electrode, which results in a positive plate havingpellets of lead dioxide, and a negative plate having pellets of metalliclead. Tetrabasic lead sulfate, 4PbO.PbSO₄, is a very useful startingmaterial for the preparation of positive electrodes for lead-acidbatteries. According to U.S. Pat. No. 3,765,943 and U.S. Pat. No.3,899,349, battery plates or electrodes fabricated with this sulfate andcured in the presence of a controlled amount of carbon dioxide gas, areassociated with an increased product yield, greater life, greaterreproducibility in the chemical and physical properties of the product,and crystal morphology more suitable for battery operation. Althoughboth positive and negative electrodes may be formed with tetrabasic leadsulfate, this material is preferably used for positive plates. See alsoPavlov, D. and Papazov, G., Journal of Applied Electrochemistry 6, 1976,pp. 339-345, as well as Pavlov, D. and Kapkov, N. J., ElectrochemicalSociety 137(1), 1990, pp. 16-28.

In the manufacturing process of lead-acid batteries, tetrabasic leadsulfate is usually produced by mixing the required amounts of leadyoxide (α and β-PbO with free lead), sulfuric acid and water. Althoughthis procedure seems to be very straightforward, several importantvariations of it have been reported, mainly in the patent literature.

For instance, U.S. Pat. No. 3,765,943 discloses a process forfabrication of positive electrodes for lead-acid batteries wherein theelectrodes arc fabricated from grids filled with paste and including thesteps of reacting orthorhombic lead oxide in an aqueous suspension withsulfuric acid at 80-100° C. to produce tetrabasic lead sulfate. Thelead-containing material contains at least 90 wt % of lead oxide, theaqueous suspension in which the reaction takes place is preacidified toa pH range of 1-3.5 prior to the addition of lead oxide and thetetrabasic lead sulfate is separated from the aqueous suspension withinone hour after complete addition of the sulfuric acid.

U.S. Pat. No. 4,324,768 discloses a process for the preparation of waterinsoluble lead compounds having a composition represented by the generalformula nPbO.PbX₂, wherein X stands for an inorganic acid radical, xindicates the valency of the radical X and n is a number of from 0 to 5,which comprises reacting lead monoxide according to the wet method withan inorganic acid or organic acid in the presence of hydroxylamine undersuch conditions that the initial pH value of the reaction system is nothigher than 7. The lead compound represented by the general formula maybe an ortho-salt such as lead chromate or a basic salt such astetrabasic lead sulfate (4PbO.PbSO₄). Further, it may be a saltcontaining at least two acid radicals, such as lead silicosulfate.

U.S. Pat. No. 5,096,611 discloses a process for making a battery pastecomprising an initial step of forming a paste mixture by reacting a leadoxide having a low free lead content with sulfuric acid in an aqueousslurry, followed by dewatering of the partially reacted slurry to obtainthe paste material. In one described embodiment, a slurry containing oneor more basic lead sulfates suitable for use as the active material inlead-acid battery electrodes is formed in a continuously stirred tankreactor. The slurry is withdrawn from the reactor and fed to a beltpress, which reduces the moisture content of the slurry to the desiredlevel. Battery pastes produced according to that invention may be fedcontinuously to a paster for mass production of positive and negativebattery plates from grids. This process can utilize a variety of leadoxides including Barton, leady and nonleady oxides of any crystalstructure, and can produce a paste containing either tribasic leadsulfate, tetrabasic lead sulfate, or a mixture thereof at a specifiedratio. The amount of tetrabasic lead sulfate in the battery paste isdetermined during paste formation, and no subsequent adjustment isneeded. Free lead can be removed or oxidized and the curing step iseliminated from the lead-acid battery manufacturing process. U.S. Pat.No. 5,290,359 discloses an apparatus for making a battery pastefollowing the process disclosed in U.S. Pat. No. 5,096,611.

U.S. Pat. No. 5,252,105 discloses a continuous process in which anelectrode for a lead-acid battery is prepared without the conventionalcuring step. The general procedure for preparing electrodes includespreparing a paste mixture comprising an active material precursor,sulfate-containing acids, and an inhibitor. The active materialprecursor includes lead oxides having at least 10% by weight lead oxidein the form of Pb₃O₄ (red lead), and a BET surface area of at leastabout 0.8 m²/g; desirably about 1.00 to 1.50 m²/grain and preferablyabout 1.0 to 1.25 m²/g. The inhibitor (preferably a simple sugar or arelated compound having at least one hydroxyl group per carbon atom)prevents formation of tribasic lead sulfate and tetrabasic lead sulfatefrom the precursor material and sulfate-containing acids, except atelevated temperatures (tetrabasic lead sulfate forms with furtherprocessing at temperatures typically in excess of 80° C.). The paste isapplied to electrode grids and reacted at elevated temperatures forbetween about 5 and about 30 minutes, to form the active material of theelectrode for both positive and negative electrodes. Plates are thenassembled into batteries and charged. Negative electrodes differ fromthe positive, mainly in the additives used.

U.S. Pat. No. 5,273,554 discloses a process for fabricating a battery inwhich tetrabasic lead sulfate is produced by reacting lead oxide with asubstantial excess of a sulfate reactant at a pH in the range of 9.3 to12. The resulting materials provide needle-like structures with a widthgenerally in the range of 3 to 1 μm. The relative narrow needles, whenemployed on the positive electrode of a lead acid battery, improve theefficiency of formation, provide good adhesive to the positive plate,extend battery life, as well as, yield excellent capacity per gram ofactive material. In one embodiment, a precursor is prepared by reactinglead oxide with sulfuric acid in the presence of an excess of sulfate toform a paste and applying the paste to a grid with subsequent curing.Control of the temperature below 60° C. in the reaction medium and ofthe sulfate excess yields, after curing at a temperature above 70° C.and 100% humidity, a positive plate having an extremely uniformprismatic size, tetrabasic lead sulfate and a uniform pore distribution.Most significantly, the width of these crystals is extremelynarrow—having an average dimension in the range of 1 to 2 μm—allowingrapid conversion to lead oxide from the precursor and further providingenhanced adhesion and current capacity attributes. Thus, the lead oxideobtained after conversion has prismatic crystals with an average crystalwidth less than 2.5 μm. In a second embodiment, tetrabasic lead sulfateof relative small prismatic size is achieved by just reacting lead oxidewith sulfuric acid in a stirred aqueous solution containing excesssulfate at temperatures above 60° C. to immediately form tetrabasic leadsulfate. The tetrabasic lead sulfate is mixed with water to form apaste. Positive plates made by applying this paste to a lead grid andconverted to lead oxide, also have higher current capacity attributes.U.S. Pat No. 5,660,600 refers to the batteries fabricated according tothe process disclosed in U.S. Pat. No. 5,273,554, as well as to thematerials useful therein.

U.S. Pat. No. 6,454,977 discloses a continuous paste making process forlead-acid batteries that includes the steps of mixing water with a leadoxide, reacting an acid (usually sulfuric acid) with the lead oxide in amixture to produce lead oxide-lead sulfate compounds, and forming apaste comprising interlocking basic lead sulfate complex crystals fromthe lead lead-oxide sulfate compounds, where the mixing, reacting, andcrystal forming steps occur in an extrusion or in a high-shearcontinuous processing apparatus. The method also includes the step ofextruding the paste from the extrusion apparatus into a grid mesh wherethe paste is dried to form a battery plate of the lead-acid battery.

Evidently, tetrabasic lead-sulfate is an essential raw material for thelead-acid battery industry. Surprisingly, only a few synthesis methods,other than the ones mentioned above, have been reported in thescientific literature for the production of tetrabasic lead sulfate.

For instance, Burbank J., Journal of The Electrochemical Society 113(1),1966, pp. 10-14, describes a method for the preparation of monobasic,tribasic and tetrabasic lead sulfates by reacting PbO and dilutesulfuric acid. The crystalline phases were identified by x-raydiffraction, and electron microscope examination showed all three toconsist of prismatic needles. The three basic sulfates were pressed intopellets and oxidized anodically in a frame of pure lead and in 1.050specific gravity sulfuric acid X-ray diffraction showed that eachtransformed to alpha lead dioxide. PbO₂ formed from pellets made fromtetrabasic lead sulfate were mechanically strong formed by theinterlocking of large crystals.

Vilhunen, Journal of Power Sources 39, 1992, pp. 59, evaluated thedifferences arising on the positive active material with high tetrabasiclead sulfate content due to preparation technique or starting material.Wet chemical analysis, X-ray diffraction, transmission and scanningelectron microscopy methods were used to characterize the materials. Thetetrabasic lead sulfate was made from leady oxide and tetragonal PbO bysolution or paste methods. The paste yielded smaller crystals which werealso more irregular than the large single crystal-like particlesresulting from the solution process. These results provide choices forachieving the crystal structure in conditional plates most conducive tolong cycle life.

Lastly, Grugeondewaele et al., Journal of Power Sources 72(2), 1998, pp.126-131, prepared tribasic lead sulfate and tetrabasic lead sulfate byreactive grinding. The effects of various experimental parameters(stoichiometry, hygrometry of the starting compounds, duration ofmechanical treatment) upon the nature and morphological features of theresulting phase were investigated. With water in excess, only tribasiclead sulfate was produced while dry reagents led to tetrabasic leadsulfate. In both case, samples with a small particle size and highreactivity were obtained. In order to evaluate the influence of themorphology upon the electrochemical performances of such grindingproduced samples, the capacity was measured and compared with that oftraditional tribasic lead sulfate and tetrabasic lead-sulfate samples.

In brief, the available methods for the production of tetrabasic leadsulfate are complex, costly or yield heterogeneous crystal sizes.

SUMMARY

An exemplary embodiment of the present invention relates to a solidstate reaction method for the production of tetrabasic lead sulfate. Themethod includes the steps of mixing a stoichiometric mixture of 4PbO andPbCO₃ and H₂SO₄ and heating the stoichiometric mixture of 4PbO and PbCO₃and H₂SO₄ at a temperature between 500 and 700° C. for 3 to 8 hours. Themethod also includes the steps of deagglomerating and sieving resultingtetrabasic lead sulfate.

Another exemplary embodiment of the present invention relates to amethod of forming a battery plate that includes mixing a stoichiometricmixture of 4PbO and PbCO₃ and H₂SO₄ and heating the stoichiometricmixture of 4PbO and PbCO₃ and H₂SO₄ and PbO at a temperature between 500and 700° C. for 3 to 8 hours. The method also includes deagglomeratingand sieving resulting tetrabasic lead sulfate. The method also includesforming a paste using the tetrabasic lead sulfate and providing thepaste on a battery plate.

Another exemplary embodiment of the present invention relates to amethod of producing a lead-acid battery that includes providing abattery comprising a plurality of battery plates, the battery platesprepared by a method comprising: mixing a stoichiometric mixture of 4PbOand PbCO₃ and H₂SO₄; heating the stoichiometric mixture of 4PbO andPbCO₃ and H₂SO₄ at a temperature between 500 and 700° C. for 3 to 8hours; and deagglomerating and sieving resulting tetrabasic leadsulfate. The method also includes forming a paste using the tetrabasiclead sulfate; and providing the paste on a battery plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a characteristic x-ray diffraction pattern for tetrabasiclead sulfate obtained by a solid state reaction according to the presentinvention.

FIG. 2 shows a characteristic scanning electron microscopy micrograph ofthe tetrabasic lead sulfate obtained by a solid state reaction accordingto the present invention.

DETAILED DESCRIPTION

The present invention relates to different methods used in theproduction of tetrabasic lead sulfate by means of solid state reactionsat high temperatures, which allow forming powdered sulfate compoundshaving a particle size of less than 10 μm. According to the presentinvention, the following methods are employed to obtain the tetrabasiclead sulfate.

4PbO+PbSO₄+thermal treatment→4PbO.PbSO₄

In this case, a solid state reaction method is proposed for theproduction of tetrabasic lad sulfate by reacting 4PbO and PbSO_(4.) Thismethod comprising the steps of mixing of the stoichiometric mixture of4PbO and PbSO₄, heating the stoichiometric mixture of 4PbO and PbSO₄ ata temperature between 500 and 700° C. during 3 to 8 hours and finallydeagglomerating and sieving the resulting tetrabasic lead sulfate.

EXAMPLE 1

Five mole of lead oxide were intimately mixed up with four mole of leadsulfate. A heat treatment of the reacting mixture at 600° C. for 4 hoursmade it possible to achieve a degree of transformation of 95%.

3PbO.PbSO₄.H₂O+PbO+thermal treatment→4PbO.PbSO₄+H₂O

In this case a solid state reaction method is proposed for theproduction of tetrabasic lead sulfate by reacting 3PbO.PbSO₄.H₂O+PbO.This method comprising the steps of mixing of the stoichiometric mixtureof 3PbO.PbSO₄.H₂O+PbO, heating the stoichiometric mixture of3PbO.PbSO₄.H₂O+PbO at a temperature between 500 and 700° C. during 3 to8 hours and finally deagglomerating and sieving the resulting tetrabasiclead sulfate.

EXAMPLE 2

A degree of transformation into tetrabasic lead sulfate of 83.4% wasachieved by heat treating at 600° C. for 5 hours a mixture of one moleof tribasic lead sulfate with one mole of lead oxide.

An alternative method to this chemical route to produce tetrabasic leadsulfate is as follows:

Either by using active materials coining from the pastes used for thepreparation of the lead-acid battery plates, or coming from recycledlead-acid battery plates. In this case, a solid state reaction method isproposed for the production of tetrabasic lead sulfate by reacting3PbO.PbSO₄.H₂O+PbO. This method comprises the steps of mixing either thepaste used for the preparation of the lead-acid battery plates, or thepaste recovered from recycled lead-acid battery plates, heating themixture at a temperature between 500 and 700° C. during 3 to 8 hours,and finally deagglomerating and sieving the resulting tetrabasic leadsulfate.

EXAMPLE 3

A degree of transformation into tetrabasic lead sulfate of 93% wasachieved by heat treating at 650° C. for 5 hours the active materialscoming from recycled lead-acid battery plates.

5PbO+H₂SO₄+thermal treatment→4PbO.PbSO₄+H₂O

In this case a solid state reaction method is proposed for theproduction of tetrabasic lead sulfate by reacting 5PbO+H₂SO₄. Thismethod comprising the steps of missing the PbO with 1 mole of a H₂SO₄aqueous solutions having a specific gravity in the range of 1.100 to1.400 g/cm³, following this by a temperature rise of the stoichiometricmixture to 500-700° C., holding the mixture at that temperature for 3 to8 hours, and finally deagglomerating and sieving the resultingtetrabasic lead sulfate.

EXAMPLE 4

A degree of transformation into tetrabasic lead sulfate of 72.9% wasachieved by heat treating at 600° C. for 6 hours a mixture of 5 mole ofPbO with 1 mole of a H₂SO₄ aqueous solution having a specific gravity of1.150 g/cm³.

4PbO+PbCO₃+H₂SO₄+thermal treatment→4PbO.PbSO₄+CO₂+H₂O

In this case, a solid state reaction method is proposed for theproduction of tetrabasic lead sulfate by reacting 4PbO+PbCO₃+H₂SO₄,comprising the steps of mixing a stoichiometric mixture of 4PbO+PbCO₃,followed by the addition of 1 mole of a H₂SO₄, aqueous solution having aspecific gravity in the range of 1.100 to 1.400 g/cm³, then heating thestoichiometric mixture of 4PbO+PbCO₃+H₂SO₄ at a temperature between 500and 700° C. for 3 to 8 hours, and finally deagglomerating and sievingthe resulting tetrabasic lead sulfate.

EXAMPLE 5

A degree of transformation into tetrabasic lead sulfate of 86% wasachieved by heat treating at 650° C. for 6 hours a mixture of 4 mole dePbO with 1 mol of PbCO₃ plus 1 mole of a H₂SO₄ aqueous solution having aspecific gravity of 1.150 g/cm³.

5PbO+(NH₄)₂SO₄+treatment→4PbO.PbSO₄+2NH₃

In this case, a solid state reaction method is proposed for theproduction of tetrabasic lead sulfate by reacting 5PbO+(NH₄)₂SO₄,comprising the steps of mixing the stoichiometric mixture of5PbO+(NH₄)₂SO₄, then heating the stoichiometric mixture of5PbO+(NH₄)₂SO₄ at a temperature between 500 and 700° C. during 3 to 8hours, and finally deagglomerating and sieving the resulting tetrabasiclead sulfate.

EXAMPLE 6

A degree of transformation into tetrabasic lead sulfate of 80% wasachieved by heat treating at 650° C. for 6 hours a mixture of 5 mole ofPbO with 1 mol of (NH₄)₂SO₄.

The characteristic X-ray diffraction angles for the tetrabasic leadsulfate obtained according to the present invention are shown in thefollowing table and the corresponding peak intensities are indicated inFIG. 1.

Corresponding Phase X-Ray Diffraction Angle (4BS = tetrabasic leadsulfate) 10.70 4BS 27.60 4BS 28.70 4BS 29.20 4BS 31.00 4BS 33.60 4BS46.00 4BS 46.50 4BS

The morphology and size of the particles obtained according to thepresent invention can be observed in FIG. 2. Procedures indicated in thepresent invention allow to obtain particles of tetrabasic lead sulfatehaving a size of less than 10 μm, avoiding any further milling of thematerial and requiring only the employment of a dispersion process,which can be carried out either under dry conditions or in a liquidsuspension.

The production of tetrabasic lead sulfate by using a wet procedureinvolves the formation of tribasic lead sulfate intermediate compound,which must be transformed later into tetrabasic lead sulfate by means ofa suitable heat treatment. In contrast, in the methods which are claimedin the present invention, the chemical reaction that takes place betweenlead oxide and different sulfated compounds occurs in a single hightemperature treatment.

The procedures indicated in the present application allow to obtainparticles of tetrabasic lead sulfate having a size of less than 10 μm,avoiding any further milling of the material and requiring only theemployment of a dispersion process, which can be carried out eitherunder dry conditions or in a liquid suspension.

In the methods which are claimed, the chemical reaction that takes placebetween lead oxide and different sulfated compounds occurs in a singlehigh temperature treatment.

Tetrabasic lead sulfate obtained according to the methods of the presentinvention can be used for the production of lead-acid battery pastes,the production of lead-acid battery plates made with said pastes, andthe production of lead-acid batteries subsequently made with them.

1. A solid state reaction method for the production of tetrabasic leadsulfate comprising the steps of: mixing a stoichiometric mixture of 4PbOand PbCO₃ and H₂SO₄; heating the stoichiometric mixture of 4PbO andPbCO₃ and H₂SO₄ at a temperature between 500 and 700° C. for 3 to 8hours; and deagglomerating and sieving resulting tetrabasic leadsulfate.
 2. The solid state reaction method of claim 1 wherein the stepof heating the stoichiometric mixture of 4PbO and PbCO₃ and H₂SO₄ isperformed for 6 hours.
 3. The solid state reaction method of claim 1wherein the step of heating the stoichiometric mixture of 4PbO and PbCO₃and H₂SO₄ is performed at a temperature of 650° C.
 4. The solid statereaction method of claim 3 wherein the step of heating thestoichiometric mixture of 4PbO and PbCO₃ and H₂SO₄ is performed for 6hours.
 5. The solid slate reaction method of claim 1 wherein thetetrabasic lead sulfate has a particle size of less than 10 μm.
 6. Thesolid state reaction method of claim 1 wherein the step ofdeagglomerating and sieving is a dispersion process.
 7. The solid statereaction method of claim 6 wherein the dispersion process is carried outunder dry conditions.
 8. The solid state reaction method of claim 6wherein the dispersion process is carried out in a liquid suspension. 9.A method of forming a battery plate comprising: mixing a stoichiometricmixture of 4PbO and PbCO₃ and H₂SO₄; heating the stoichiometric mixtureof 4PbO and PbCO₃ and H₂SO₄ at a temperature between 500 and 700° C. for3 to 8 hours; and deagglomerating and sieving resulting tetrabasic leadsulfate; forming a paste using the tetrabasic lead sulfate; andproviding the paste on a battery plate.
 10. The method of claim 9wherein the step of heating the stoichiometric mixture of 4PbO and PbCO₃and H₂SO₄ is performed at a temperature of 650° C.
 11. The method ofclaim 10 wherein the step of heating the stoichiometric mixture of 4PbOand PbCO₃ and H₂SO₄ is performed for 6 hours.
 12. The method of claim 9wherein the tetrabasic lead sulfate has a particle size of less than 10μm.
 13. The method of claim 9 wherein the step of deagglomerating andsieving is a dispersion process.
 14. The method of claim 13 wherein thedispersion process is carried out under dry conditions.
 15. The methodof claim 13 wherein the dispersion process is carried out in a liquidsuspension.
 16. A method of producing a lead-acid battery comprising:providing a battery comprising a plurality of battery plates, thebattery plates prepared by a method comprising: mixing a stoichiometricmixture of 4PbO and PbCO₃ and H₂SO₄; heating the stoichiometric mixtureof 4PbO and PbCO₃ and H₂SO₄ at a temperature between 500 and 700° C. for3 to 8 hours; deagglomerating and sieving resulting tetrabasic leadsulfate; forming a paste using the tetrabasic lead sulfate; andproviding the paste on a battery plate.
 17. The method of claim 16wherein the step of heating the stoichiometric mixture of 4PbO and PbCO₃and H₂SO₄ is performed at a temperature of 650° C.
 18. The method ofclaim 17 wherein the step of heating the stoichiometric mixture of 4PbOand PbCO₃ and H₂SO₄ is performed for 6 hours.
 19. The method of claim 16wherein the tetrabasic lead sulfate has a particle size of less than 10μm.
 20. The method of claim 16 wherein the step of deagglomerating andsieving is a dispersion process.